Flexible thermoelectric devices, methods of preparation thereof, and methods of recovering waste heat therewith

ABSTRACT

The present disclosure relates to flexible thermoelectric devices. In some embodiments, such devices can comprise a flexible substrate with a first conductive component and a second, different conductive component deposited thereon so as to form a plurality of electrical junctions. The flexible substrate can be a fabric, and the conductive component can be deposited by methods such as stitching of conductive yarns or deposition of conductive inks. The present disclosure further relates to methods of preparing flexible thermoelectric devices and methods of utilizing flexible thermoelectric devices for producing electrical current from waste heat.

FIELD OF THE DISCLOSURE

The present disclosure relates to flexible platforms for heat recovery,and particularly relates to flexible thermoelectric devices and methodsof manufacture thereof.

BACKGROUND

Many processes, industrial and biological, produce waste heat. Wasteheat recovery methods previously implemented by various industries haveincluded heat-to-heat technologies that transfer heat from unwantedplaces to processes or locations where thermal input is needed andheat-to-power technologies that convert heat to energy (e.g.,electricity).

Heat-to-heat technologies include heat exchangers and preheaters, andsuch technologies are commonly implemented in high temperature(e.g., >650° C.) processes, such as melting furnaces and incinerators,to transfer exhausted heat to other fluid streams. As temperaturedecreases, however, heat transfer kinetics slow, and larger surfaceareas are required to maintain efficiency. Low temperature heat flowsare also often not useful for industrial processes, necessitating anupgrade using additional equipment such as a heat pump. As a result,heat exchanger technology is uncommon for heat streams of <150° C.

At more moderate temperatures (e.g., 250° C. to 650° C.), heat-to-powertechnologies can be used, such as in systems implementing Rankine powercycles. Steam turbines are common examples of such technology, andtypical steam turbines using water as the working fluid can only operateefficiently above about 350° C. Although organic Rankine cycles (using alower boiling organic material with as the working fluid) can achieveefficiencies of 10-20% below 250° C., specific optimization is typicallyrequired, and the organic working fluid raises toxicity, flammability,explosivity, and environmental concerns.

Relatively few options are presently known for recovering lowtemperature (e.g., <250° C.) waste heat. Examples of known sources oflow temperature waste heat (and the typical temperature range of thewaste heat) include steam boiler exhaust (150-260° C.), exhaust gas fromrecovery devices (70-250° C.), process steam condensates (50-90° C.),cooling water return (30-250° C.), and drying/baking ovens (90-250° C.).Computing data centers are further sources of low temperature wasteheat, and for example, exhaust air from data racks can produce fluidtemperatures of about 50-100° C. above ambient. Although microscaledevices (e.g., thin film thermoelectric modules) have shown promise atthe microchip level, no effective macroscale solution is presentlyknown. There remains a need in the art for further options for recoveryof low temperature waste heat.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to thermoelectric (TE) devices. Thedisclosure particular provides flexible platforms for TE devices thatenable the devices to partially or substantially conform to the shape ofa heat source around which the flexible TE device may be partially orcompletely wrapped.

In some embodiments, flexible thermoelectric devices according to thepresent disclosure can comprise a flexible substrate with a firstconductive component and a second, different conductive componentdeposited thereon so as to form a plurality of electrical junctions. Infurther embodiments, a flexible thermoelectric device according to thepresent disclosure can be defined by one or more of the followingstatements. It is understood that any combination of the followingstatements is encompassed by the present disclosure.

The flexible substrate can define a first surface spaced apart from asecond surface, and the plurality of electrical junctions can bepositioned at the respective surfaces in an alternating fashion.

The electrical junctions positioned at the first surface can beseparated from the junctions positioned at the second surface with anelectrically insulating medium.

The plurality of electrical junctions can define a plurality ofthermopiles.

The flexible substrate can be formed of a fibrous material.

The flexible substrate can be a woven fabric or a non-woven fabric.

The flexible substrate can be a polymeric film.

The flexible substrate can be formed of a natural or synthetic material.

The flexible substrate can comprise a material selected from the groupconsisting of polyesters, cotton, polyamides, poly-N-vinylcarbazole,cellulosic materials, polyvinyl alcohol, polypropylene, polyethyleneterephthalate, fiberglass, and combinations thereof.

The substrate can be one or both of molded and folded.

The substrate can include one or more cuts or perforations.

One or both of the first conductive component and the second conductivecomponent can be a conductive thread or yarn.

One or both of the first conductive component and the second conductivecomponent can be a conductive ink.

One or both of the first conductive component and the second conductivecomponent can comprise conductive particles and a carrier.

The first conductive component can have a positive or negative Seebeckcoefficient and the second conductive component can have a Seebeckcoefficient of opposing sign.

The first conductive component and the second conductive component canhave respective Seebeck coefficients that differ by at least 25, by atleast 50, by at least 75, or by at least 100.

In further embodiments, the present disclosure further relates tomethods of forming a thermoelectric device. The formed TE device can bedefined by any of the statements above in any combination and/or anyfurther disclosure provided herein. In exemplary embodiments, methods offorming a flexible TE device can comprise depositing a first conductivecomponent and a second, different conductive component on a flexiblesubstrate so as to form a plurality of electrical junctions. In furtherembodiments, methods of forming flexible TE device according to thepresent disclosure can be defined by one or more of the followingstatements. It is understood that any combination of the followingstatements is encompassed by the present disclosure.

The flexible substrate can define a first surface spaced apart from asecond surface, and the first and second conductive components can bedeposited such that the plurality of electrical junctions are positionedat the respective surfaces in an alternating fashion.

The method can comprise one or both of molding and folding the flexiblesubstrate one or both of before and after depositing the first andsecond conductive components.

Depositing one or both of the first and second conductive components cancomprise stitching a conductive thread or yarn to the flexiblesubstrate.

Depositing one or both of the first and second conductive components cancomprise applying a conductive ink to the flexible substrate.

In other embodiments, the present disclosure relates to methods ofproducing electrical current from waste heat. Such methods can compriseapplying a flexible thermoelectric device as otherwise described hereinto a source of waste heat. In particular, the methods can comprisepartially or substantially conforming the flexible thermoelectric deviceto the source of waste heat. For example, the flexible thermoelectricdevice can be conformed to curved surfaces or cylindrical surfaces, aswell as being conformed to substantially planar surfaces, which mayinclude one or more non-planar portions.

The foregoing provides a summary of the present disclosure and is not tobe considered limiting of the various further embodiments that may beencompassed by the further disclosure provided herein. The nature of theflexible TE devices, methods of preparation of such devices, and methodsof using such devices should thus be construed in light of the entiretyof the present disclosure with reference to the non-limiting embodimentsand examples provided herein.

BRIEF DESCRIPTION OF THE FIGURES

Having thus described the disclosure in the foregoing Summary, referencewill now be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

FIG. 1 is an illustration of a thermoelectric module showing anexemplary combination of a plurality of TE elements of opposite sign inelectrical series and thermally in parallel;

FIG. 2a is an illustration of an exemplary stitching type that may beused in forming a flexible TE device according to an embodiment of thepresent disclosure;

FIG. 2b is an illustration of another exemplary stitching type that maybe used in forming a flexible TB device according to an embodiment ofthe present disclosure;

FIG. 3 is an illustration of alternating junctions of positive andnegative Seebeck coefficient connected electrically in series andthermally in parallel for generation of electrical current from atemperature differential according to an exemplary embodiment of thepresent disclosure;

FIG. 4a is an illustration of a flexible TE device according to thepresent disclosure utilized in waste heat recovery in an exemplary steamturbine design;

FIG. 4b is an exploded view of the flexible TE device shown in FIG. 4 a;

FIG. 4c is an illustration of an exemplary structure of a flexible TEdevice according to the present disclosure showing the combination ofthe flexible substrate and the first electrically conductive componentand the second electrically conductive material, wherein theelectrically conductive components comprise first and second metallicyarns stitched into the flexible substrate;

FIG. 4d is an illustration of another exemplary structure of a flexibleTE device according to the present disclosure showing the combination ofthe flexible substrate and the first electrically conductive componentand the second electrically conductive material, wherein theelectrically conductive components comprise first and second conductiveinks deposited onto the flexible substrate;

FIG. 4e is an illustration of a further exemplary structure of aflexible TE device according to the present disclosure showing thecombination of the flexible substrate and the first electricallyconductive component and the second electrically conductive material,wherein the electrically conductive components are present in a binaryconductive thread stitched into the flexible substrate;

FIG. 5a is an illustration of design for an exemplary thermopileconstruction in a flexible TE device according to the presentdisclosure;

FIG. 5b is an image of a flexible TE device according to an exemplaryembodiment of the present disclosure wherein 12 thermopiles (24junctions) are present in a zigzag pattern on a nonwoven nylonsubstrate, the thermopiles being formed from a first ink comprisingnickel particles and a second ink comprising silver coated copperparticles; and

FIG. 6 is a graph showing the potential formed on the orthogonal sidesof the flexible TE device illustrated in FIG. 5b while one side of thedevice was heated and the opposing side was maintained in an ice bath,wherein the potential measurement was made with increasing temperaturefrom the 0° C. reference.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to exemplary embodiments thereof. These exemplary embodimentsare described so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Indeed, the disclosure may be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. As used in the specification, andin the appended claims, the singular forms “a”, “an”, “the”, includeplural referents unless the context clearly dictates otherwise.

Thermoelectrics (TE) are solid state devices that utilize thethermoelectric effect for the direct conversion of thermal energy (i.e.,temperature differences) to electricity. As such, a thermoelectric cancreate voltage when there is a temperature differential across thedevice. Thermoelectrics thus utilize the Seebeck effect, and the figureof merit for a TE is described by the value ZT according to Equation 1below.

$\begin{matrix}{{ZT} = \frac{S^{2}\sigma\; T}{\Lambda}} & {{Equation}\mspace{14mu} 1}\end{matrix}$In Equation 1, S is the Seebeck coefficient, σ is electricalconductivity, Λ is the thermal conductivity, and T is temperature. HighZT values indicate higher efficiencies. Thus, good TE materials have ahigh Seebeck coefficient and electrical conductivity but are thermalinsulators. Because electronic conductivity contributes to thermalconductivity, semiconductors are typically thought of as being good TEmaterials. TE device structures are typically designed using two TEmaterials of opposite Seebeck coefficients connected electrically inseries and thermally in parallel. Such structure is illustrated inFIG. 1. Common arrangements use junctions of n- and p-typesemiconductors.

Known thermoelectrics include rigid semiconductor modules that aretypically complex and expensive to manufacture, such as TEs based uponPbTe and SiGe. Such devices have been used extensively in powergeneration applications on space crafts showing potential for exhaustrecovery over temperature ranges of 300-600° C. and 500-1000° C.,respectively. Efficiencies for such known TE devices are generally low(e.g., approximately 8% or less at a temperature differential of 250°C.), and such efficiencies are further sharply reduced as thetemperature differential is lowered.

Thin film TE modules have previously been manufactured using standardmicroelectronics technology but are limited to low power applicationssince TE modules must maintain a sizable temperature gradient to operateat high efficiencies regardless of the ZT value. For example, a thinfilm superlattice with a ZT value of approximately 2.4 (at 300 K) and athermal conductivity of ˜0.002 W cm⁻¹ K⁻¹ as reported byVenkatasubramian (Nature, 413, 2001), in light of Fourier's Law, must beat least 5 mm thick to maintain the 250° C. temperature differencenecessary to reach the 1 W/cm² output of a typical bulk Bi₂Te₃ based TEdevices. The described superlattices, however, were approximately 5 μmin thickness, or approximately three orders of magnitude smaller thanthat required as calculated above. Nanostructuring also has beenexamined as a tool to reduce a material's thermal conductivity andincrease its ZT value; however, costly materials and expensive epitaxialgrowth methods that are required to produce such materials haveprevented significant development of such technology.

According to the present disclosure, it has been discovered thatthermoelectric devices suitable for low temperature waste heat recoverycan be provided in a flexible platform that overcomes problems in theknown field. In various aspects, the present disclosure relates toflexible thermoelectric devices that can be prepared by patterningelectrically conductive junctions on a flexible substrate, such as atextile. The use of a flexible substrate makes the flexible TE suitablefor integration with a heat source in a manner whereby it is closelyconfigured to the shape and contours of the heat source. Thermaldifferences between junctions facing the heat source and the contact andjunction facing the lower temperature condition (e.g., atmosphericconditions) results in the formation of useable energy driven by thethermoelectric effect.

Any flexible material may be utilized as a substrate for a TE deviceaccording to the present disclosure. A flexible material can be anymaterial with sufficient flexibility to allow for bending of thefinished TE device. In some embodiments, a flexible substrate can besufficiently flexible to form a bend of at least 10 degrees, a bend ofat least 30 degrees, a bend of at least 45 degrees, a bend of at least70 degrees, or a bend of at least 90 degrees. Such flexibility likewisecan apply to the finished flexible TE device. The flexible substrateand/or the flexible TE device may be elastic and/or may exhibit shapememory so that after partially or substantially conforming to a specificshape, the flexible substrate or device substantially maintains thespecific shape permanently or until otherwise re-shaped. The flexiblesubstrate and/or the TE device may partially or substantially conformnaturally (i.e., without added assistance) or may partially orsubstantially conform upon application of pressure or the like to thesubstrate. The flexible TE device, for example can exhibit sufficientmechanical flexibility for partially or substantially conformal wrappingover non-planar surfaces and thus improve thermal contact between theflexible TE device and the covered surface.

In some embodiments textiles can be particularly advantageous in lightof the high throughput manufacturing that is available. Textiles can beadvantageous substrates in light of their insulating properties. Anyflexible material (particularly any textile) that does not melt ordegrade at temperatures up to about 350° C., up to about 300° C., or upto about 250° C. may be useful according to the present disclosure.Non-limiting examples of materials that may be used in a TE devicesubstrate include polyesters, cotton, polyamides, poly-N-vinylcarbazole,cellulosic materials (e.g., cellulose triacetate), polyvinyl alcohol,polypropylene, polyethylene terephthalate, and fiberglass.

The flexible substrate can vary in thickness. For example, in someembodiments, a flexible substrate can have a thickness of greater than 1cm, greater than 2.5 cm, greater than 5 cm, or greater than 10 cm. Theflexible substrate can be substantially continuous or can be comprisedof a plurality of substrates that are one or both of electrically andphysically combined. The flexible substrate can be textured and/orcontoured. For example, the flexible substrate can be molded or pleated,and specific curves or pleats may be configured in relation to theposition of one or more thermopile junctions on the substrate. Texturingand/or contouring of the flexible substrate can be useful to provide forplacement of hot and cold junctions spaced apart with air functioning asan insulation barrier between the junctions. The flexible substrate canbe substantially impermeable, can have a defined porosity, or cancomprise one or more openings therethrough. The flexible substrate canbe formed of a single layer or a plurality of layers of the samematerial or different materials.

The flexible substrate can comprise one or more surface finishes. Insome embodiments, a coating may be applied to the flexible substratebefore or after application of the electrically conductive components.For example, a flexible TE device can include an epoxy finish or thelike to substantially encase the device.

In some embodiments, a flexible TE according to the present disclosurecan comprise a thermopile configuration based on the thermoelectricvoltage between two electrically conductive materials with oppositeSeebeck coefficients. For example, the thermopile can comprise aplurality of thermocouples connected in series or in parallel. Thethermopile configuration can be particularly useful for incorporationwith a flexible substrate, such as a textile, because of the ease ofcombination of the technologies. In some embodiments, the thermopile canbe formed on a surface of a flexible substrate. For example, thethermopile can be applied to the substrate via conductive ink printingor by otherwise affixing an electrically conductive material to thesubstrate. In other embodiments, the thermopile can be formedsimultaneously with the flexible substrate. For example, electricallyconductive filaments or yarns can be woven into a textile or can beincluded in the formation of a nonwoven substrate. In some embodiments,embroidery can be used to combine an electrically conductive materialwith the flexible substrate. Electrically conductive filaments and/oryarns can be formed in some embodiments by electrodeposition of thinfilm coatings

In some embodiments, stitching can be used to deposit an electricallyconductive component on a flexible substrate. Stitching is intended toencompass sewing, embroidering, and all other types of needle workwhereby a thread or yarn is combined with a substrate. A stitch patterncan be configured to achieve low line resistance on a substrate. Closeand overlapping stitch patterns can be useful to increase the conductorcontent per given length, resulting in a corresponding decrease inresistance. Non-limiting examples of stitching types that are suited forformation of thermopile junctions using yarns of materials of twodissimilar conductors (e.g., metals) include those described in ASTMD6193-97, such stitch types 304 and 312 shown in FIGS. 2a and 2b ,respectively. Stitching may be carried out using known industrialprocess, such as processes utilized in the quilting insulationfabrication industries.

In some embodiments, a conductive thread or yarn can be combined withnon-conductive threads or yarns to form a patterned, flexible substratecomprising the conductive component. For example, a thread or yarn canbe woven directly into a fabric during formation of the fabric ratherthan being added to a previously formed fabric or other substrate.

Conductive inks useful for printing or otherwise applying to a surfaceof a flexible substrate can include any material in a liquid stateadapted for deposition and including electrically conductive components.For example, suitable conductive inks can comprise a carrier andconductive particles, such as nano-to-micro sized metallic particles.The carrier may be formed of or otherwise include a binder configured tomaintain the conductive particles in the deposited pattern. The binderparticularly can be configured to provide for flexibility of thedeposited conductive ink after drying. The process by which theconductive ink is deposited can vary based on the carrier viscosity. Inexemplary embodiments ink jet printing can be used for low viscosityinks, and screen printing can be used for more viscous inks. Preferably,the overall conductive ink composition applied to the flexible substrateexhibits a resistance that is sufficiently close to the resistance ofthe bulk conductive component. For example, the resistance of theconductive ink can be no more 2 orders of magnitude or no more than oneorder of magnitude greater than the resistance of the bulk conductivecomponent (e.g., the bulk metal particles).

Useful conductive elements can be selected in some embodiments basedupon their Seebeck coefficient values. A flexible TE device can includea first electrically conductive component and a second electricallyconductive component, the electrically conductive components havingSeebeck coefficients of opposite sign. Metals can have either a positiveor negative Seebeck coefficient based on how effectively phonons scatterelectron transport. In metals where electrons are not stronglyscattered, the higher velocity of hot-side electrons causes theelectrons to diffuse to the cold side, thus generating a negativeSeebeck coefficient. In metals where phonon scattering of electronictransport increases sufficiently with temperature to limit mean freepath, electron diffusion occurs from the cold side to the hot side andthe Seebeck coefficient in positive. Non-limiting examples of metalswith positive Seebeck coefficients that may be useful in forming aflexible TE device according to the present disclosure include thefollowing (with the Seebeck coefficient in μV/° C.): silver (1.51),copper (1.83), gold (1.94), molybdenum (5.6), titanium (9.1), iron (15),chromium (21.8), Chromel (90Ni/10Cr) (22), Nichrome (80Ni/20Cr) (25),and Tellurium (500). Non-limiting examples of metals with negativeSeebeck coefficients that may be useful in forming a flexible TE deviceaccording to the present disclosure include the following (with theSeebeck coefficient in μV/° C.): tin (−1.0), lead (−1.05) aluminum(−1.66), manganese (−9.8), palladium (−10.7), scandium (−19), nickel(−19.5), cobalt (−30.8), Constantan (55Cu/45Ni) (−39), and bismuth(−72). A flexible TE device can comprise a first electrically conductivecomponent and a second conductive component with respective Seebeckcoefficients that are sufficiently different to provide the desired TEgeneration. For example, in some embodiments, the Seebeck coefficient ofthe second electrically conductive component can differ from the Seebeckcoefficient of the first electrically conductive component by at least25, by at least 50, by at least 75, or by at least 100. Thus, theSeebeck coefficient of the electrically conductive components can beboth positive or can be both positive. Alternatively the Seebeckcoefficient of one electrically conductive component can be positive andthe Seebeck coefficient of the other electrically conductive componentcan be negative.

A flexible TE device according to the present disclosure can comprise aplurality of junctions of two electrically conductive components ofopposite sign. In some embodiments, the two electrically conductivecomponents can be connected electrically in series and thermally inparallel, as illustrated in FIG. 3. The present TE devices particularlycan comprise a plurality of thermopiles, wherein a single thermopilecomprises back-to-back junctions of the first and second electricallyconductive components. In particular, the first junction in a thermopilecan be positioned at the hot side of the TE device, and the secondjunction in a thermopile can be positioned at the cold side of the TEdevice. Thus, the present TE device can comprise a plurality ofthermopiles connected electrically in series. In some embodiments, eachjunction can have a resistance of about 0.001 to about 0.1 Ohms.

The flexible TE devices can be configured to achieve a definetemperature gradient relative to the source of the low grade heat. Forexample, when applied to a 200° C. heat source, the flexible TE devicecan achieve a temperature gradient of about 100° C. to about 175° C. Invarious embodiments, the temperature gradient across the flexible TEdevice can be about 50% to about 90% of the temperature of the heatsource.

Flexible TE devices according to the present disclosure can provide manyadvantages of known TE technologies while also providing the ability forhigh volume, low cost production. In some embodiments, a flexible TEdevice can be configured to substantially mimic known insulationtechnologies, thus providing for seamless integration into industrialsettings where insulation is already utilized to reduce heat loss. Thepresent flexible TE devices are thus adaptable to both high and lowvolume facilities with both continuous and non-continuous heat flows.

Exemplary embodiments of flexible TE devices according to the presentdisclosure and their use in converting waste heat to electrical energyare illustrated in FIGS. 4a through 4e . Specifically, FIG. 4aillustrates the application of a flexible TE device for recovering lowtemperature heat from cooling water in a steam turbine condenser whereinthe flexible TE device is wrapped around an inlet pipe for hot waterinto the condenser. FIG. 4b shows a cut-away illustration of the pipewith the flexible TE device wrapped therearound and includes across-sectional that is illustrated in three exemplary embodiments inFIGS. 4c -4 e.

Although FIG. 4a exemplifies recovering waste heat from industrialequipment, the present disclosure is not limited to such uses. Anysource of low grade heat can be a source of heat for recovery.Specifically, the heat source can be any source at a temperature greaterthan ambient and up to about 300° C., up to about 250° C., or up toabout 200° C. In some embodiments, the low grade heat source cancomprise organic sources, including mammals, such as humans. Forexample, a flexible TE device according to the present disclosure can bean article of clothing. In such embodiments, the flexible TE clothingcan be configured to produce electricity safely in amounts sufficient topower medical devices, sensors, and the like and/or charge externalelectrical devices (e.g., mobile phones or similar devices).

In the embodiment of FIG. 4c , a first metallic yarn and a secondmetallic yarn having differing Seebeck coefficients as described hereinare stitched onto a flexible substrate (fabric) in a pattern forming aseries of thermopile junctions. As illustrated, a plurality of stitchedflexible substrates are combined with electrically insulating spacers toform the overall flexible TE device. If desired, an insulating layer maybe included around one or both of the inner edges and the outer edges ofthe layered substrates thus forming opposing faces in thermal connectionwith the heated pipe (inner edges) and the cooler atmosphere (outeredges). In the embodiment of FIG. 4d , a first conductive ink and asecond conductive ink having differing Seebeck coefficients aredeposited on the surface of a flexible substrate (fabric) that is shapedsuch that alternating junctions of the formed thermopiles are positionedadjacent the heat source and the intervening junctions of the formedthermopiles are positioned in the cooler, surrounding atmosphere. Theflexible substrate may be molded into the exemplified shape or may bepleated. A variety of shapes may be utilized, and the exemplifiedstar-type pattern is non-limiting. A plurality of flexible TE devicesmay be combined, as illustrated. In the embodiment of FIG. 4e , a binaryconductive thread is stitched through a flexible substrate so as to formalternating thermopile junctions at a first surface that is positionedadjacent the heat source and at a second, opposing surface in thecooler, surrounding atmosphere.

The flexible TE device can be provided in a variety of shapes and sizesand can be customized to the shape and size of the respective materialto which it is to be applied. In some embodiments (See FIG. 4c and FIG.4d ) the flexible TE device can be configured as an elongated strip thatis greater in length than in width. In some embodiments, the flexible TEdevice can be configured as a tape and may include an adhesive or otherattachment element if desired. Such elongated strips or tapes can bewrapped around the heat source, for example, in a spiral fashion.

EXPERIMENTAL

The present invention will now be described with specific reference tothe following example, which are not intended to be limiting of theinvention and are rather provided to show exemplary embodiments.

A flexible TE device was prepared using a non-woven nylon substrate.Nickel and copper conductive lines were screen-printed onto thesubstrate in a zigzagged pattern to form a series of thermopilejunctions. The conceptual design of the test and the formed test patternare illustrated in FIG. 5a and FIG. 5b , respectively. The so-madeflexible TE device was formed of 12 thermopiles with a total of 24junctions.

The formed TE device was heated on one side with a hot-plate while theopposite end was held at 0° C. with an ice water bath. The test devicehad a line resistance of 220Ω and generated approximately 9 mV at a ΔTof approximately 150° C. This equates to a maximum power ofapproximately 0.4 μW. The voltage output was also observed to be linearwith the temperature gradient, as expected for a thermopile device (seethe graph of FIG. 6).

Many modifications and other embodiments of the disclosure will come tomind to one skilled in the art to which this disclosure pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments disclosedherein and that modifications and other embodiments are intended to beincluded within the scope of the appended claims. Although specificterms are employed herein, they are used in a generic and descriptivesense only and not for purposes of limitation.

The invention claimed is:
 1. A flexible thermoelectric devicecomprising: a flexible, non-woven textile substrate formed of a fibrousmaterial and having an inner face and an opposing, outer face that isspaced apart from the inner face, the non-woven textile substrate beingsufficiently flexible to form a bend of at least 30 degrees; a firstconductive component; and a second, different conductive component;wherein the first conductive component and the second, differentconductive component each comprise a conductive thread or yarn that isstitched through the flexible, non-woven textile substrate from theinner face to the opposing, outer face so that the first conductivecomponent and the second, different conductive component form aplurality of alternating electrical junctions on the inner face and onthe opposing, outer face of the flexible, non-woven textile substrate;and wherein flexible thermoelectric device exhibits sufficientmechanical flexibility for partial or substantial conformal wrappingover non-planar surfaces.
 2. The flexible thermoelectric deviceaccording to claim 1, wherein the plurality of electrical junctions onthe inner face are separated from the plurality of electrical junctionson the outer face with an electrically insulating medium.
 3. Theflexible thermoelectric device according to claim 1, wherein theplurality of electrical junctions define a plurality of thermopiles. 4.The flexible thermoelectric device according to claim 1, wherein theflexible, non-woven textile substrate comprises a fibrous materialselected from the group consisting of polyesters, cotton, polyamides,poly-N-vinylcarbazole, cellulosic materials, polyvinyl alcohol,polypropylene, polyethylene terephthalate, fiberglass, and combinationsthereof.
 5. The flexible thermoelectric device according to claim 1,wherein the first conductive component has a positive or negativeSeebeck coefficient and the second conductive component has a Seebeckcoefficient of opposing sign.
 6. The flexible thermoelectric deviceaccording to claim 1, wherein the first conductive component and thesecond, different conductive component are in the form of a binaryconductive thread.
 7. The flexible thermoelectric device according toclaim 1, wherein the flexible, non-woven textile substrate has athickness of greater than 1 cm.
 8. The flexible thermoelectric deviceaccording to claim 1, wherein the flexible, non-woven textile substratehas a thickness of greater than 2.5 cm.
 9. A method of forming athermoelectric device comprising adding a first conductive component anda second, different conductive component to a previously formedflexible, non-woven textile substrate formed of a fibrous material andhaving an inner face and an opposing, outer face, wherein the non-woventextile substrate is sufficiently flexible to form a bend of at least 30degrees, and wherein the first conductive component and the second,different conductive component each comprise a conductive thread oryarn, and the method comprises stitching the conductive thread or yarnthrough the flexible, non-woven textile substrate from the inner face tothe opposing, outer face so as to form a plurality of alternatingelectrical junctions on the inner face and on the outer face of theflexible, non-woven textile substrate; wherein the formed thermoelectricdevice exhibits sufficient mechanical flexibility for partial orsubstantial conformal wrapping over non-planar surfaces.
 10. The methodof claim 9, wherein the flexible, non-woven textile substrate has athickness of greater than 2.5 cm.